During the exploitation of such yarns, the following three methods are known to introduce PVA (polyvinyl alcohol) fibers into the center of cotton yarns via a ring spinning system.
The first method is a spinning process in which PVA fibers are put into the core of cotton yarns on a spring frame, and PVA spun yarns are embedded into the streams of cotton fibers in a drafting zone during spinning Since the cotton fibers in the outer sheath are likely to cluster into bundles during the weaving process, PVA fibers are unevenly spread on the surface of the yarns, resulting in uneven thickness of the yarns and thus insufficient hollowness and softness of towels made of such yarns.
The second method is a spinning process in which PVA fiber slivers (formed by carding) are put into the center of cotton slivers (formed by carding) in a drawing process of a spinning system for purpose of blending. It is unable to ensure that PVA fibers will be evenly wrapped by cotton fibers to form a hollow structure, even if the fibers are evenly blended in this process.
The third method is a process in which PVA slivers are embedded into the center of cotton slivers at a feeding end of the drafting zone of a roving frame, twisted on the roving frame, and then spun. After tests and a number of improvements, this method is regarded as the most hopeful method for achieving hollow PVA. However, only a single-hole hollow structure may be formed due to the restriction of the process.
The present invention provides a method for successively putting water soluble fibers into natural fibers (e.g. cotton) to produce a hollow and ultra soft structure, by putting water soluble slivers into the center of a multi-hole feeder with multiple cotton fiber slivers arranged around the water soluble fiber in a pre-drawing process via a multi-hole sliver feeder.